In electrostatographic imaging and recording processes, such as electrophotographic printing, an electrostatic latent image is formed on a primary image-forming member such as a photoconductive surface and is developed with a thermoplastic toner powder to form a toner image. The toner image is thereafter transferred to a receiver member, e.g., a sheet of paper or plastic, and the toner image is subsequently fused to the receiver member in a fusing station using heat and/or pressure. The fuser member can be a roller, belt, or any surface having a suitable shape for fixing thermoplastic toner powder to the receiver member. Fusing is commonly accomplished by passing the toned receiver member between a pair of engaged rollers that produce an area of pressure contact known as a fusing nip. In order to form the nip, at least one of the rollers typically has a compliant or conformable layer on its surface. Heat is transferred from at least one of the rollers to the toner in the fusing nip, causing the toner to partially melt and attach to the receiver member. Where the fuser member is a heated roller, it is generally desirable for it to have a smooth surface in contact with the toner. Where the fuser member is in the form of a belt, e.g., a flexible endless belt that passes around a heated roller, it typically has a smooth, hardened outer surface.
In most fusing stations utilizing a fuser roller and an engaged pressure roller, it is common for one of the two rollers to be rotated by any suitable mechanism, the other roller being counter-rotated by frictional forces in the nip.
In a simplex roller fuser, toner is attached or fixed to one side of a receiver member at a time. In this type of fuser, the roller that contacts the unfused toner, herein called the “fuser roller”, is usually actively heated. The roller that contacts the other side of the receiver member, herein called the “pressure roller”, is usually not directly heated. Either or both rollers can have a compliant layer on or near the surface for forming a fusing nip of useful width.
In a duplex fusing station, which is less common, two toner images are simultaneously attached, one to each side of a receiver member passing through a fusing nip. In such a duplex fusing station there is no real distinction between fuser roller and pressure roller, both rollers performing similar functions, i.e., providing heat and pressure.
Two basic types of simplex roller fusers have evolved. One type uses a compliant pressure roller to form the fusing nip against a hard fuser roller. The other type uses a compliant fuser roller to form the nip against a hard pressure roller. (A roller designated herein as “compliant” includes a conformable layer or cushion layer typically having a thickness greater than about 2 mm and in some cases exceeding 25 mm; a roller designated as “hard” includes a rigid cylinder which typically has thereon a relatively thin polymeric or resilient elastomeric coating, typically less than about 1.25 mm thick).
A conventional fuser roller includes a cylindrical core member, often metallic such as aluminum, coated with one or more synthetic layers which typically include polymeric materials made from elastomers.
The most common type of fuser roller includes an internal source of heat. Such an internally-heated fuser roller normally has a hollow core, inside of which is located a heating source, usually a lamp. The cushion layer surrounding the core of a compliant fuser roller is an elastomeric layer through which heat is conducted from the core to the surface, and the elastomeric layer typically contains fillers for enhanced thermal conductivity.
An externally-heated fuser roller is also known, typically heated by surface contact between the fuser roller and one or more heating rollers pressed against the fuser roller.
A typical belt fuser can embody a heated roller around which is entrained a closed-loop belt under tension, the heated roller forming a fusing nip with a pressure roller such that the belt is captured in the nip and thereby indirectly heated. During fusing, the unfused toner on a receiver member is in contact with the indirectly heated belt.
In certain fusing stations a belt can be provided entrained around a pressure roller, which belt is captured in a fusing nip between the pressure roller and a heated fuser roller and helps to move a receiver member through the fusing nip.
To create high quality multicolor toner images, small toner particles are used having diameters less than about 10 micrometers, and the receiver members, typically papers, are smooth and can be coated papers. A typical method of making a multicolor toner image involves trichromatic color synthesis by subtractive color formation. In such synthesis, successive imagewise electrostatic images, each representing a different color, are developed with a respective toner of a different color. Typically, the colors correspond to each of the three subtractive primary colors (cyan, magenta, and yellow) and, optionally, black. As described for example in the Herrick et al. patent (U.S. Pat. No. 6,016,415), an electrophotographic printer apparatus can include a series of tandem modules wherein color separation images are formed and transferred in register to a receiver member being moved through the apparatus while supported on a transport web. An unfused toner image formed thereby on the receiver member is subsequently moved to a fusing station for fusing therein.
To rival the photographic quality of glossy prints produced using silver halide technology, it is desirable that multicolor toner images have suitable glossiness. The amount of gloss depends on the material characteristics of the toner, the smoothness of the fuser member, the pressure in the fusing nip, and on the temperature of the fusing station. In particular, a uniform glossing level depends on the ability of a heated fuser member to provide a suitably rapid response time, e.g., for overcoming fluctuations in the demand for heat as receiver members are moved through the fusing station, or during cycle-up from a cold start to operating temperature.
The degree of gloss or gloss level of a toner image can be quantitatively measured in a standard way using a specular glossmeter, for example by the method described in ASTM-D523-67. Typically, a single reflectivity measurement is made which measures the amount of light from a standard source which is specularly reflected in a defined path. A suitable device for this purpose is a Glossgard II 60° glossmeter (available commercially from Pacific Scientific Inc., Silver Springs, Md.) which produces a reading, on a standardized scale, of a specularly reflected beam of light having angles of incidence and reflection of 60° to the normal. The glossmeter can measure gloss levels representing a dull matte to a very shiny finish. The usual range of measured gloss numbers on the meter is between 0 and 100, the instrument being normally calibrated or adjusted so that the upper limit corresponds to a surface that has substantially less than the complete specular reflection of a true mirror. Thus extremely smooth glossy surfaces can have gloss levels in excess of 100. Reflectivity readings are indicated as G60 gloss numbers (gloss levels). The larger the G60 number, the glossier the toner image.
The area of contact between a conformable fuser roller and a toner-bearing surface of a receiver sheet as it passes through the fusing nip is determined not only by the pressure exerted in the nip but also by the characteristics of the cushion layer (preferably located on the fuser roller). The extent of the contact area helps establish the length of time that any given portion of the toner image will be in contact with and heated by the fuser roller, and is an important variable dictating the amount of heat generated in the fusing station and carried away by receiver members.
To monitor the temperature of a fuser member, at least one temperature sensor is typically mounted in association with the fuser member. The sensor sends electronic information relating to the temperature of the member to a microprocessor, for example, or to a logic and control unit (LCU). Thus for example a thermistor can be used mounted in direct contact with a thermally conductive core member of a fuser roller. Any suitable temperature-sensing device can be employed in order to create a precalibrated electronic signal for continuous monitoring of the temperature of the fuser member.
As disclosed in the Dodge et al. patent (U.S. Pat. No. 4,415,800), the temperature of a fuser roller in a fusing station can be controlled via a microcomputer utilizing signals sent by a temperature sensor for sensing the temperature of the fuser roller at a predetermined time. In particular, temperature-versus-time profiles can be measured during heating of a roller to operating temperature, e.g., from a start-up cold temperature or from some warm (or hot) initial temperature remaining after a temporary shutdown of the fusing station. Error messages can be displayed and/or the fusing station automatically shut down if there is inappropriate behavior of the roller, such as may be caused by a malfunction resulting in overheating or underheating relative to the (predetermined) operating temperature.
For use in a fusing station employing a heated fuser roller, it is known to have on hand several variations of fuser rollers having different surface finishes, which rollers can be interchangeably installed for purpose of producing different gloss levels in fused toner images. Thus one type of fuser roller can be used for jobs requiring a matte finish (little or no gloss), another type of fuser roller used for medium gloss, and a third type used for making high gloss toner images. Typically, matte images are text images having for example all-black text, whilst high gloss images are for pictorial imaging, particularly for photographic quality imaging on smooth papers. If a fuser roller needs to be replaced or exchanged, e.g., when a new job stream requires a certain type of fuser roller which is different from that already mounted in the fusing station, the mounted fuser roller is removed, e.g., manually, and replaced by another fuser roller so as to provide a different surface finish. The source of heat for fusing is then powered up so as to raise the temperature of the newly installed fuser roller to a suitable (predetermined) operating temperature, i.e., for the type of output finish required for fused toner images of the new job stream.
There is a need for a low cost way to validate that a newly installed fuser roller is of a presumptive type, with the further objects of minimizing human error or loss of time as could occur if an operator manually installs the wrong type of fuser roller, or if an operator fails to properly select the respective operating set points needed for a given type of fuser roller. The present invention provides a reliable, inexpensive, validation method. Moreover, a newly installed fuser roller of a given type may exhibit a particular heating behavior that is not within specification, e.g., because other devices are adjacent to or contact the fuser roller in the fusing station. Thus there is a need to measure this heating behavior, and the invention provides a simple way to validate that a newly installed fuser roller has a heating behavior commensurate with specification.